back up for master branch
Merge pull request #1 from emstoudenmire/master

Adding valid() and index(n) methods to NDIterator.
Merge github.com:naokin/BTAS-TWG into devel
Updated Tensor and TArray classes, cleaned up file structure
Renew NDIterator class to be more readable and user-friendly, I hope
Merge 'naoki/master'
Removed out-of-date code introduced in patch to old version of NDIterator.
Minor cleanup of external begin and end NDIterator friend functions.
Added friend declaration and changed template argument to allow conversion between NDIterators with convertible iterator types.